This invention relates generally to the field of liquid infusion devices for medical applications. More specifically, it relates to mechanically-driven infusion devices used for the administration of a liquid medicament to a patient from a filled syringe into an intravenous (IV) administration system.
Various devices have been developed for the intravenous (IV) infusion of liquid medicaments into a patient at a controlled flow rate over an extended period of time. For example, gravity flow IV administration sets have been employed for many years, and more recently, IV administration sets with electrically powered pumps have been developed.
There are applications in which a more compact and inexpensive type of infusion device is desired or required. For example, in addition to direct infusion from a syringe, it is frequently necessary to infuse a secondary fluid into a primary IV flow from a gravity flow or electrically-pumped IV administration set. Also, infusion into an ambulatory patient frequently requires an infusion device that is less bulky, less complex, and easier to use than gravity flow or pump-powered devices. For such applications, relatively complex self-powered infusion devices are frequently used.
With a typical, manually actuated IV administration syringe, infusion over an extended period of time is usually impractical or inconvenient. Furthermore, even among syringes of the same size from the same manufacturer, the actuation forces required to provide a given fluid flow-versus-time profile vary greatly from syringe to syringe. Consequently, it is necessary to provide a sufficiently high actuation force to achieve a substantial degree of uniformity in fluid delivery from syringe to syringe. It has proven difficult consistently to achieve such sufficiently high syringe actuation forces with manually actuated syringes.
To overcome these problems, the prior art has devised a variety of mechanisms for increasing the actuation force on the syringe throughout the infusion process. One type of syringe actuation mechanism is that which utilizes either internal or external springs to displace the plunger of the syringe. Examples of such mechanisms are shown in the following U.S. Pat. Nos.:2,472,116--Maynes; 2,565,081--Maynes; 2,591,457--Maynes; 3,880,163--Ritterskamp; 3,882,863--Sarnoff et al.; 4,381,006--Genese; 4,530,695--Phillips et al.; 4,597,754--Thill et al.; 4,623,330--Laby et al.; 4,755,172--Baldwin; 4,966,585--Gangemi; 4,997,420--LeFevre; 5,078,679--Reese; 5,100,389--Vaillancourt; 5,178,609--Ishikawa; 5,318,539--O'Neil; 5,320,609--Haber et al.; 5,330,430--Sullivan; 5,383,858--Reilly et al.; and 5,599,315--McPhee. Another example is shown in European Patent Application Publication No. 584 569 A2.
The known prior art devices suffer from one or more shortcomings, however. For example, several of the above-listed patents show the use of "constant force" springs, which are elongated flat leaf springs coiled on a drum. Such springs, however, add expense, bulk, and mechanical complexity to the device.
Another drawback of some prior art devices is that a relatively great physical effort is required to compress the plunger actuation spring, because these devices lack a sufficient mechanical advantage to reduce the "loading effort" any appreciable degree. Other syringe actuation devices of the prior art require the syringe to be disconnected from any downstream fluid conduits (such as an IV administration set) before being loaded into the actuation device. This limitation makes such devices disadvantageous for use in those clinical applications, such as IV administration procedures, in which it is advantageous to load a pre-filled syringe into the syringe actuation device while the syringe is connected to the IV conduit.
It would therefore be a significant advancement over the prior art to provide a spring-actuated infusion syringe that overcomes the aforementioned limitations. Specifically, it would be advantageous to provide such a device that yields improved uniformity in syringe-to-syringe fluid flow rates without a mechanism of undue complexity. Furthermore, it would be advantageous to provide such a syringe that may be filled and spring-loaded without undue physical effort, and without disconnecting it from a downstream conduit.